1. Field of the Invention
The present invention relates to portable ventilator systems used in transporting critically ill patients, and more particularly, to a system of dual sets of oxygen tanks delivering oxygen to a high-flow switchover manifold apparatus.
2. Description of the Related Art
Critically ill patients with respiratory failure require mechanical, assisted ventilation. When they are being transported to and from the hospital, for example in an ambulance or helicopter, such patients are typically given ventilatory assistance manually by means of a bag mask (e.g., Ambu(trademark) bag) and 100% oxygen delivered from an oxygen tank. Such a bag mask consists of a face mask that fits over the patient""s nose and mouth, and an attached hand-held bag for manually inflating and deflating the patient""s lungs. Such bag-mask ventilation is inherently unreliable because it depends on the skill and judgment of the operator of the bag mask to inflate and deflate the patient""s lungs at the proper frequency and tidal volume. As a result, wide interoperator variation is observed in a given patient""s delivered tidal volume and respiratory rate. In addition, wide intraoperator variation is also observed from patient to patient by the same operator because of differences in patient size, lung compliance, and other factors.
This means that the patient may be over- or underventilated, depending on the minute ventilation, which is the product of respiratory rate and tidal lung volume, being delivered by the operator. As a result, significant hypercapnia from CO2 retention by the patient, with concomitant respiratory acidosis; or hypocapnia, with concomitant respiratory alkalosis, may occur. When respiratory acidosis occurs as the result of underventilation, it compounds any underlying metabolic acidosis, such as lactic acidosis caused by poor tissue oxygenation (which is nearly always present in patients with respiratory failure), or diabetic ketoacidosis caused by inadequate insulin availability. In transport situations, this problem is worsened, as the acid-base balance and oxygenation status of the patient are unknown because one cannot readily perform an arterial blood gas analysis in the field.
In addition to the inherent unreliability of operating a bag mask, there is a significant risk to the patient of barotrauma, including pneumothorax, pneumomediastinum, and subcutaneous emphysema. These complications occur primarily when relatively noncompliant lungs are overinflated, with resulting small perforations in the pleura, alveoli, or other pulmonary structures.
One problem with using mechanical ventilators in transport settings, for example in an ambulance, is that such ventilators typically require oxygen flow pressures around 40 lbs. per square inch (xe2x80x9cpsixe2x80x9d), which is the typical oxygen pressure in oxygen delivery systems within the walls of hospitals. Normally, ventilators are in fact connected to wall-oxygen systems in hospitals and nursing homes. Even portable ventilators, such as the VDR-3C Universal Logistical Precussionator Ventilator, available from Percussionaire Corporation, is designed for use with low-pressure (e.g., 40 psi) oxygen delivery systems. Oxygen tanks, on the other hand, although portable, deliver oxygen at pressures typically from 100 to 2,200 psi, which is too high for delivery to mechanical ventilators.
In addition, there is a problem in delivering adequate quantities of oxygen for prolonged transport using a mechanical ventilator. Typically, one or two oxygen tanks will not last a sufficiently long period to allow patients to be mechanically ventilated with a moderate to high fraction of inspired oxygen (xe2x80x9cFI02xe2x80x9d) (e.g., 100% FI02) over the course of a trip of, for example, 20 -40 minutes duration.
The present invention addresses the need for an oxygen delivery system that can enable high-flow, high-pressure oxygen tanks to be adapted to portable mechanical ventilators, and that will allow sufficient oxygen to be administered throughout the course of prolonged transport of a patient while retaining portability.
There is provided in accordance with one aspect of the present invention an oxygen delivery system for portable mechanical ventilation. The oxygen delivery system includes at least a first set and a second set of individual oxygen tanks. A first intake tube is interposed between the first set of oxygen tanks and a first regulator, and the first regulator contains a valve which remains open until the pressure of oxygen flowing through the first regulator drops below a predetermined threshold pressure level. A second intake tube is interposed between the second set of oxygen tanks and a second regulator, and the second regulator contains a valve which remains closed until the pressure in the second regulator drops to approximately the predetermined threshold pressure level. One or more outtake tubes connect the first and second regulators, and a central tube is interposed between these outtake tubes and a mechanical ventilator.
In accordance with one aspect of the present invention, the threshold pressure level is within the range of 90 to 100 pounds per square inch. In a firther aspect of the present invention, there are only two sets of oxygen tanks.
In a further aspect of the present invention, one or more pressure gauges are attached to the regulators. In other aspects of the present invention, one or more pressure gauges are attached to the central tube and measure the pressure of oxygen flowing to the mechanical ventilator.
In accordance with another aspect of the present invention, there is provided a method of delivering oxygen to a portable ventilator during transport of a patient. The method includes providing a first set of oxygen tanks connected by tubing to a first regulator, and providing a second set of oxygen tanks connected by tubing to a second regulator. The method further includes causing a valve within the first regulator to close when the oxygen pressure within the first regulator drops below a particular pressure threshold, thereby causing the flow of oxygen through the first regulator to cease; and causing a valve within the second regulator to open at approximately the same threshold pressure, thereby causing oxygen to flow from the second set of oxygen tanks through the second regulator to the patient""s ventilator.